The increasing miniaturization of semiconductor elements (the increasingly high degree of integration of semiconductor devices) has led to the use of multilevel interconnect structures on semiconductor substrates. In order to reduce parasitic capacitance between conductors, material consisting mainly of silicon oxide is generally used for the insulating layers in such semiconductor devices.
Insulating thins films of silica are known for use as protective layers and as insulating layers in electronic devices. The use of wet-coating compositions to form the layers is generally well known. For example, U.S. Pat. No. 4,756,977 teaches a process for coating electronic devices with a silica thin film by applying a solvent solution of hydrogen silsesquioxane resin on a substrate, evaporating the solvent, and then heating at temperatures of 150.degree. C. to 1000.degree. C. to effect conversion into ceramic like silica.
It is also known that the dielectric constant of the insulating thin film can be reduced by executing the insulating thin film itself as a porous structure. For example, U.S. Pat. No. 5,548,159 has described the formation of an insulating thin film with a porous structure through the use of the baked product of hydrogen silsesquioxane resin as the dielectric layer in a highly integrated circuit. This patent, however, does not disclose a specific method for the formation of the porous structure.
Because the miniaturization of semiconductor elements leads to increasingly small interconnect gaps and increasingly high aspect ratios between interconnects, large film thicknesses and an excellent capacity to fill between interconnects are required of the insulating layers. Highly integrated circuits with interconnect gaps declining below 0.18 .mu.m have been designed for semiconductor devices in recent years. While highly integrated circuits of this type require that the dielectric constant of the insulating layers be brought below 2.7, even insulating layers formed from hydrogen silsequioxane resin have been unable to achieve such dielectric constants.
An object of this invention is to provide a process for forming insulating thin films that have a low dielectric constant.
A further object of this invention is to provide semiconductor devices having low dielectric constant insulating layers therein and to the method for the fabrication thereof.